<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .a {
            width: 200px;
            height: 300px;
            background-color: #f00;
            float: left;
        }

        .b {
            /* calc css3计算属性  可以接受数学表达式  +  -  *  /    */

            /* width: -webkit-calc(100% - 200px); */
            width: calc(100% - 200px);
            height: 400px;
            background-color: #000;
            float: right;


            /* display: flex;
            display: -webkit-flex; */
        }
    </style>
</head>

<body>
    <div class="a"></div>
    <div class="b"></div>
</body>

</html>